Glaciers in Equilibrium, McMurdo Dry Valleys, Antarctica

The McMurdo Dry Valleys are a cold, dry polar desert and the alpine glaciers therein exhibit small annual and seasonal mass balances, ofte

Quantifying 20th Century Glacier Change in the Sierra Nevada, California

Numerous small alpine glaciers occupy the high elevation regions of the central and southern Sierra Nevada, California. An inventory based on 1:24,000 topographic maps revealed 1719 glaciers and perennial snowfields for a total area of 39.15 +/- 0.13 km(2). The number of \u27true\u27 glaciers, versus non-moving ice, is estimated to be 122 covering 14.89 +/- 0.08 km(2) or 38% of the ice-covered area. Historic photographs, geologic evidence, and field mapping were used to determine the magnitude of area change over the past century at 14 glaciers. The area change between 1903 and 2004 ranged from -31% to -78%, averaging -55%. Based on these values rough estimates of volume change suggest an ice volume loss from 1903 (1.09 km(3)) to 2004 (0.43 km(3)) of 0.66 km(3) (0.59 km(3) water). Rapid retreat occurred over the first half of the 20th century beginning in the 1920s and continued through the 1960s after which recession ceased by the early 1980s and some glaciers advanced. Since the late 1980s glaciers resumed retreat with a rapid acceleration starting in the early 2000s. The relatively uniform timing of area changes in the study glaciers is a response to regional climate whereas the magnitude of change is influenced by local topographic effects. Area changes correlate significantly with changes in summer and winter air temperatures. Warmer winter temperatures warm the snowpack lengthening the summer melt season. Spring air temperatures and precipitation may also play an important role. The occurrence of spring snowfall can delay the onset of melt due to the increased surface albedo. Examining the influence of topographic variables we only found headwall height at the top of the glacier to show an influence on glacier change. Higher headwalls shadow the glacier from solar radiation reducing melt and enhancing snow accumulation via avalanching. If the glaciers continue to shrink at current (1972-2004) rates, most will disappear in 50-250 years

Do Cryoconite Holes Have the Potential to be Significant Sources of C, N, and P to Downstream Depauperate Ecosystems of Taylor Valley, Antarctica?

Nutrient recycling occurs in hydrologically isolated cryoconite holes on the glaciers of the McMurdo Dry Valleys, Antarctica. Biogeochemical processes enrich the cryoconite holes with solute and nutrients compared to the source sediment and glacier ice. The position of the glacier within the landscape affects the physical and biogeochemical character of the cryoconite holes, with those found in more biologically productive areas of the valley having higher concentrations of C, N, and P and higher pH. Comprehensive assessment of the quality and quantity of bioavailable C, N, and P shows that the cryoconite holes represent a significant store of nutrient in this depauperate landscape, since the total mass of C and N is similar to that found in the ephemeral streams. The dissolved nutrients within the holes, and a significant proportion of the particulate store, are released to the valley ecosystem via the network of ephemeral streams and perennially ice-covered lakes as a result of hydrological connection with the supraglacial drainage system. In most cases, cryoconite holes are flushed every several years, but during warm periods which occur with near decadal frequency, all holes connect and flush their contents off the glaciers. Simple mass balance modeling shows that an increase in primary productivity observed in Lake Fryxell that followed such a melt event in 2001/2002 can be explained by an influx of nutrients (specifically N) generated in the cryoconite holes. These features are hence an integral part of the Dry Valley ecosystem and should be considered in models of downstream biological processes

Quantifying Twentieth Century Glacier Change in the Sierra Nevada, California

Numerous small alpine glaciers occupy the high elevation regions of the central and southern Siena Nevada, California. These glaciers change size in response to variations in climate and are therefore important indicators of climate change. An inventory based on USGS topographic maps (l :24,000) revealed 1719 glaciers and perennial snow and ice features for a total area of 39.l5 ±7.52 km2. The number of \u27true\u27 glaciers, versus non-moving ice, is estimated to be 118, covering 15.87 ± 1.69 Km2. All glaciers were located on north to northeast aspects, at elevations \u3e3000 m. Historical photographs, geologic evidence, and field mapping were used to determine the magnitude of area loss over the past century at 14 glaciers. These glaciers decreased in area by 31% to 78%, averaging 55%. The rate of area change was determined for multiple time periods for a subset of seven glaciers. Rapid retreat occurred over the first half of the twentieth century beginning in the 1920s in response to warm/dry conditions and continued through the mid-1970s. Recession ceased during the early 1980s, when some glaciers advanced. Since the 1980s each of the seven study glaciers resumed retreat. The uniform timing of changes in area amongst study glaciers suggests a response to regional climate, while the magnitude of change is influenced by local topographic effects. Glacier area changes correlate with changes in spring and summer air temperatures. Winter precipitation is statistically unrelated to changes in glacier area. Headwall cliffs above the glaciers alter the glacier responses by reducing incoming shortwave radiation and enhancing snow accumulation via avalanching

The Geography of Glaciers and Perennial Snowfields in the American West

A comprehensive mid-20th century inventory of glaciers and perennial snowfields (G&PS) was compiled for the American West, west of the 100° meridian. The inventory was derived from U.S. Geological Survey 1:24,000 topographic maps based on aerial photographs acquired during 35 years, 1955–1990, of which the first 20 years or more was a cool period with little glacier change. The mapped features were filtered for those greater than 0.01 km2. Results show that 5036 G&PS (672 km2, 14 km3) populate eight states, of which about 1276 (554 km2, 12 km3) are glaciers. Uncertainty is estimated at ±9% for area and ±20% for volume. Two populations of G&PS were identified based on air temperature and precipitation. The larger is found in a maritime climate of the Pacific Northwest, characterized by warm winter air temperatures and high winter precipitation (~2100 mm). The other population is continental in climate, characterized by cold winter air temperatures, relatively low winter precipitation (~880 mm), and located at higher elevations elsewhere. The G&PS in the Pacific Northwest, especially in the Olympic Mountains, are particularly vulnerable to warming winter air temperatures that will change the phase of winter precipitation from snow to rain, further accelerating glacier shrinkage in the future. Comparison with a recent inventory suggests that the total G&PS area in the American West may have decreased by as much as 39% since the mid-20th century

Biogeochemical Evolution of Cryoconite Holes on Canada Glacier, Taylor Valley, Antarctica

The cryoconite holes of the McMurdo Dry Valleys are simple, closed biogeochemical systems involving water, ice, mineral and organic debris, which serve as ecosystems for consortia of microorganisms. This study is the first to document the seasonal and annual chemical evolution of solutes in cryoconite holes. Samples of glacier ice, frozen cryoconite holes and those containing water were collected during the austral summer of 2005–2006. The isolation age was calculated from the excess Cl‾ in the holes, and varied from 0 to 5 years (a), consistent with the last hot summer when the cryoconite holes were open to the atmosphere. The holes progressively deepen with isolation age. Variations in DIC, DOC, K⁺ and SO²⁻₄ suggest that dissolution of primary minerals in the cryoconite debris, cyclical precipitation and dissolution of secondary carbonates, net photosynthesis over summer and net respiration during the autumnal freeze are the principal reactions which perturb the seasonal and annual solute concentrations in the holes. DOC is generated in the holes at a rate of 7.5 μg C cm⁻² a⁻¹, and non-sea-salt K⁺ accumulates in frozen holes at a rate of 0.073 μeq cm⁻² a⁻¹. We infer that C cycling is complex even in these otherwise simple systems

Data From: The Geography of Glaciers and Perennial Snowfields in the American West

A comprehensive mid-20th century inventory of glaciers and perennial snowfields (G&PS) was compiled for the American West, west of the 100° meridian. The inventory was derived from U.S. Geological Survey 1:24,000 topographic maps based on aerial photographs acquired during 35 years,1955–1990